Shells of various cross-sectional shapes (e.g., oval or irregular shapes) are used in many products, such as automotive mufflers. Typically, the shell is elongate, and one or more end caps are mechanically locked (or secured) to the shell by a process known as seaming (or lockseaming), to form a housing defining one or more chambers therein. As is well known in the art, the process involves rotating the body portion and end caps around a central axis and engaging the end caps with forming rollers. Typically, two forming rollers (e.g., a curling roller and a flattening roller) are used to perform two forming operations sequentially. These are generally referred to as the curling and flattening operations respectively. However, the prior art seaming processes do not necessarily include both the curling and flattening operations.
A typical seaming process involving the curling and flattening operations on shells with oval or irregular shapes and the apparatus therefor is illustrated in FIGS. 1A-1C, 2, and 3. (The balance of the drawings illustrate the invention herein.) In the typical seaming process, an end cap flange 10 of an end cap 12 and a shell flange 11 on a shell 13 (FIG. 1A) are formed into a lock seam portion 14 (FIG. 1C), as shown in FIGS. 1A-1C. As can be seen in FIG. 1A, in the prior art, the end cap 12 is positioned on a mandrel 17 in tooling 18 (FIG. 2). Also, the end cap 12 is adapted to receive at least a part of the shell 13 thereon to locate the shell flange 11 in a predetermined position relative to the end cap flange 10, so that a lip portion 19 is thereby defined (FIG. 1A).
For example, the end cap flange 10 typically has a length “L1” of approximately 0.625-0.75 inches (16-19 mm.), and the typical shell flange has a length “L2” of approximately 0.234-0.273 inches (6-7 mm.) (FIG. 1A). Accordingly, the end cap flange 10 typically is about 10 mm. longer than the shell flange 11. Also, when the shell flange 11 is in the predetermined position relative to the end cap flange 10, the flanges 11, 10 are substantially abutting each other.
Once the end cap 12 is on the tooling 18 and the shell 13 is properly positioned on the end cap 12 and the tooling 18, the tooling 18 is rotated about a central axis 24 thereof (FIGS. 2, 3).
Next, a curling roller 22 is engaged with the lip portion 19. While the tooling 18 is rotated about the axis 24 thereof, the curling roller 22 is urged against the lip portion 19, i.e., in the direction indicated by arrow “A”.
As a result of the engagement of the curling roller 22 with it, the lip portion 19 is thereby formed into a curled portion 26 (FIG. 1B), i.e., the curling operation is then completed. Next, the flattening operation is performed. Typically, while the tooling 18 is rotating, a flattening roller 28 is urged against the curled portion 26 (i.e., in the direction indicated by arrow “B” in FIG. 1C), pressing the curled portion 26 against the shell 13 to form the curled portion 26 into the lock seam portion 14 (FIG. 1C).
It will also be understood that another end cap typically is also secured at the other end of the shell 13. To simplify the illustration, only the attachment of one end cap 12 to the shell 13 is shown. A housing 27 is formed when one or more end caps (i.e., as the case may be) are secured to the shell 13 (FIG. 1C).
As can be seen in FIG. 1A, the curling roller 22 includes an engagement surface 23 with which the lip portion 19 is engaged. The engagement surface 23 is designed to form the lip portion 19 into the curled portion 26. Also, and as can be seen in FIG. 1C, the flattening roller 28 includes an engagement surface 29 for engaging the curled portion 26, and forming the curled portion 26 into the lock seam portion 14.
As is well known in the art, various approaches may be taken to forming the lock seam portion. For example, instead of a curling operation and a flattening operation, the seaming process may involve two curling operations. The foregoing description of the curling and flattening operations is only one example of the prior art seaming process. Accordingly, for the purposes hereof, the curled portion is considered to be a modified lip portion.
In FIGS. 2 and 3, the apparatus of the prior art for performing the prior art seaming process is shown. The prior art apparatus includes the tooling 18 which has an inner cam track 30 with an inner cam surface 31. As can be seen in FIG. 2, the tooling 18 also includes an outer cam track 32 with an outer cam surface 35. The inner cam track 30 has substantially the same shape as the end cap's outline, but the inner cam track 30 is smaller than the end cap 12, and fits inside the end cap 12.
In the prior art process, the tooling 18 is rotated around the central axis 24, i.e., in the direction indicated by arrow “C”. Cam followers 38a, 38b are positioned between the inner cam track 30 and the outer cam track 32, and engage the inner and outer cam track surfaces 31, 35 while the tooling 18 rotates. As can be seen in FIGS. 2 and 3, the cam followers 38a, 38b are rotatably mounted on main arms 40a, 40b. The main arms 40a, 40b oscillate around shaft points 42, 44 respectively as the tooling 18 rotates. While the tooling 18 rotates, the centers of the cam followers 38a, 38b substantially follow a path 45 approximately midway between the inner and outer cam surfaces 31, 35.
The prior art apparatus also typically includes forming rollers 48a, 48b which are also mounted on arms 34a, 34b respectively. Each arm 34a, 34b is rotatable around a pivot point 36a, 36b respectively, and the arms 34a, 34b are powered by hydraulic cylinders 46a, 46b respectively. The hydraulic cylinders 46a, 46b are adapted to move the arms 34a, 34b between a retracted position (shown in FIGS. 2, 3) and an extended position (not shown).
In the prior art, the forming rollers 48a, 48b typically are positioned substantially at 180° apart from each other. Also, as can be seen in FIGS. 2 and 3, the main arms 40a, 40b typically are positioned so as to substantially “mirror” each other.
As indicated in FIGS. 2 and 3, the end cap 12 is placed on the mandrel 17, so that the end cap 12 is supported thereon, and a part of the shell is positioned on the end cap. While the tooling 18 rotates about the center 24, the main arms 40a, 40b oscillate and the cam followers 38a, 38b are generally maintained on the path 45 by the inner and outer cam tracks 30, 34. As is known, the cam followers 38a, 38b are rotatably mounted on the main arms 40a, 40b. Also, the forming rollers 48a, 48b are connected to the main arms 40a, 40b respectively, in two places namely: (i) via the hydraulic cylinders 46a, 46b; and (ii) via the pivot points 36a, 36b. In this way, the forming rollers 48a, 48b are indirectly supported by the cam followers 38a, 38b. The forming rollers 48a, 48b engage the lip portion 10, ultimately forming the lip portion 10 into the lock seam portion.
For clarity of illustration, an original edge 16 (i.e., an initial edge thereof, prior to engagement of the lip portion 19 by the forming rollers) of the lip portion 19 is shown in dashed outline. Also, the lock seam portion 14 is shown in solid outline, to simplify the illustration. It will be evident to those skilled in the art that FIGS. 2 and 3 generally show the end cap 12 after the seaming process has been completed.
For example, when the tooling 18 rotates from the position shown in FIG. 2 to the position shown in FIG. 3, the main arms 40a, 40b both pivot inwardly about the shaft points 42, 44 respectively (i.e., in the directions indicated by arrows “D” and “E” respectively), substantially simultaneously. Similarly, when the tooling 18 rotates from its position as shown in FIG. 3 to its position shown in FIG. 2, the main arms 40a, 40b pivot outwardly (i.e., in the directions as indicated by arrows “F” and “G”), substantially simultaneously.
The prior art has a number of disadvantages. For instance, the prior art tooling is required to be very heavy and, as a result, is relatively expensive. In addition, because of the large mass of the tooling, changing the tooling is difficult, and therefore the process of changing the tooling (which is required to be done from time to time) is also relatively expensive. As is well known in the art, the tooling 18 preferably is rotated relatively rapidly, e.g., about 60 rpm. Because of this, oscillation of the arms 40a, 40b is relatively rapid, subjecting the main arms 40a, 40b to relatively high rates of acceleration and deceleration.
Accordingly, a relatively large amount of power is required to operate the prior art apparatus. During operation, the tooling 18 is rotated at a substantially constant speed. First, power (i.e., torque) is required to rotate the tooling 18, and second, power is required to position the main arms 40a, 40b to form the lip portion 10 into the lock seam portion 14, to secure the end cap 12 to the shell 13.
Yet another disadvantage of the prior art apparatus is the significant noise resulting from the operation thereof. The noise generally results from shifts in pressure exerted by the cam followers 38a, 38b, i.e., the cam followers 38a, 38b alternately pressing primarily first on the inner cam track surface and next on the outer cam track surface and vice versa, while the tooling 18 rotates.